It's not just athletes who use steroids to build up their bodies. The muscle culture among gay men is leading many to quietly exploit the drugs while ignoring the potential side-effects.

As the Olympics demonstrated, steroids and sport still go hand-in-hand for those athletes who seek a short-cut to glory. The drugs' ability to build muscle, and so deliver better results, is now widely known.

But among gay men anabolic steroids first became common for health rather than vanity reasons. In the 1980s, doctors prescribed them as a way to combat AIDS-related weight loss, to complement a gym regime.

Some HIV+ men still have them prescribed today. But "anabolics" have developed more into a drug of choice than necessity.

The growing muscle culture in the gay scene has seen a thriving black market emerge as men seek a quick route to the "body beautiful".

This has provoked the NHS into action with a conference, believed to be the first of its kind, in London later this month to find out more about the relationship between gay men and steroids.

I have an image in my head of what I want to look like and who I want to attract

"When I look in the mirror I think: 'I want to get bigger.' I have an image in my head of what I want to look like and who I want to attract."

Dr Sean Cummings, who runs a private gay clinic called Freedom Health in central London, says a third of his patients admit to steroid use, and numbers are increasing sharply.

Core users tend to be professionals, aged from late 30s to early 50s, he says.

"It's not the young disco bunnies but men going through a mid-life crisis. A lot of them tend to think it's now or never. They build their bodies up to attract a particular type of man and look a particular way."

Anabolic steroids are the synthetic version of the male sex hormone testosterone. They increase the capacity of the muscles to build protein, store energy and absorb oxygen.

Each user responds differently but among the more severe side-effects are a thickening of the blood, enlarged prostate and accelerated hair loss.

Testicles can shrink temporarily and breasts can become feminised if the body compensates by over-producing oestrogen.

Muscle culture has become a part of a diverse gay scene

A psychological side-effect is a condition called "bigorexia" when muscular men see themselves as thinner than they really are and are scared of losing weight.

"Although side effects are often minor, breast development in a man who wants big pecs isn't ideal," says Dr Cummings.

Instead, his major concerns are about the source, dosage and purity of the steroids, as well as worries about injecting - the risk of passing on HIV through shared needles is seen as one of the most serious concerns.

Downer

Dr Pierre Bouloux, a hormones specialist, treats men with low testosterone levels and says steroid abuse is "huge". He wants to see recreational use of steroids stigmatised.

"After a course of steroids, the user has a downer and there's a plunge in psyche so instead of giving the body a rest, they want to do it again," says Dr Bouloux.

"It's a vicious circle and I see this in ordinary gyms too. It's not just a gay thing. There are gyms full of people doing nothing but this."

While not unsafe compared to many other drugs on the street, he wants the NHS to highlight the dangers in an effort to shame users.

Dr Cummings believes his approach is more open-minded. He prefers to talk through the issues with patients who want advice and offers blood tests to check their organs. Some are put off starting steroids when they hear about the side effects, he says.

But some in the gay community believe the issue is could be overplayed.

Richard Smith, senior associate editor of Gay Times, plans to tell the conference that the muscle culture makes up only a small part of the diverse gay community.

"Not every gay man goes clubbing and to the gym. That's only a tiny minority," he says.